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JUL  2  4  JQTK 

UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


BULLETIN  No.  180 


OBSERVATIONS  AND  EXPERIMENTS  ON 
THE  SAN  JOSE  SCALE 


BY  STEPHEN  A.  FORBES 
STATE  ENTOMOLOGIST 


URBANA,  ILLINOIS,  MARCH,  1915 


BY  STEPHEN  A.  FOEBES,  STATE  ENTOMOLOGIST 

The  product  of  a  considerable  amount  of  field  and  laboratory 
work  on  the  San  Jose  scale,  much  of  which  was  done  or  begun  under 
the  immediate  supervision  of  Jas.  A.  West,  of  my  office  staff,  has 
lain  for  some  time  in  the  form  of  field  notes  and  unfinished  manu- 
script prepared  by  Mr.  West  before  his  lamented  death  in  1909.  Lapse 
of  time  and  the  studies  of  others  have  made  some  of  this  material  obso- 
lete; but  such  part  of  it  as  is  here  presented  seems  still  useful  and 
worthy  of  publication.  The  larger  part  of  this  paper  relates,  indeed,  to 
a  series  of  experiments  not  yet  finished  in  1909,  but  continued  for  two 
years  thereafter,  and  reported  now  from  the  original  field  notes  made 
partly  by  Mr.  West,  but  mainly  by  W.  P.  Flint  and  L.  M.  Smith, 
who  were  his  aids  also  in  the  earlier  work. 

THE  SAN  JOSE  SCALE  ON  FRUITS 

The  San  Jose  scale  infests  not  only  the  trunk,  limbs,  and  leaves, 
but  also  the  fruit  of  trees,  often  so  marking  the  fruit  as  to  make  it 
unfit  for  sale.  The  danger  of  dissemination  by  this  means  is,  how- 
ever, very  slight,  since  the  fruit  itself  or  the  parings  from  it  are 
little  likely  to  be  so  placed  that  young  insects  from  them  can  secure 
a  lodgment  or  a  suitable  breeding-place.  Our  attention  was  especially 
called  to  this  subject  by  a  statement  made  in  a  bulletin  of  the  Divi- 
sion of  Zoology  of  the  Pennsylvania  State  Department  of  Agriculture 
(Vol.  IV,  No.  7,  November,  1906)  which  says,  referring  to  the  San 
Jose  scale :  "Its  abundance  upon  fruit  of  any  kind  need  not  be  con- 
sidered alarming,  as  it  can  not  possibly  spread  from  fruit  that  has 
begun  to  ripen,  because  it  dies  on  such  fruits  and  can  not  reproduce 
from  them.  In  Bulletin  No.  8  of  the  same  series,  the  same  writer 
says:  "This  pest  dies  upon  the  fruit  as  soon  as  it  ripens,  and  con- 
sequently there  is  no  danger  of  disseminating  or  spreading  it  by  this 
means. ' ' 

October  3,  1906,  Mr.  West  obtained  three  ripe  Jonathan  apples 
infested  by  the  San  Jose  scale  and  kept  them  under  observation  on 
his  office  table.  The  scale  multiplied  readily  on  all  of  them.  One 
of  the  apples  was  kept  until  November  29,  at  which  time  there  were 
more  than  thrice  as  many  well-developed  San  Jose  scales  on  it  as  in 
the  beginning,  and  most  of  them  were  alive.  There  were  also  many 


546  BULLETIN  No.  180  [March, 

newly  set  young  upon  it,  and  crawling  young  were  seen  just  before 
it  was  peeled  and  eaten. 

December  11,  1907,  two  infested  Ben  Davis  apples  were  taken 
from  a  package  which  had  been  in  cold  storage,  and  were  placed  in 
a  warm  room.  Crawling  young  appeared  on  them  after  ten  or  twelve 
days,  and  some  of  these  set  and  began  to  develop.  One  of  these  apples 
was  kept  two  weeks  and  the  other  twenty-six  days,  and  on  the  twenty- 
fifth  day  three  crawling  young  were  seen. 

THE  LIFE  HISTORY  OF  THE  SAN  JOSE  SCALE  IN  ILLINOIS 

The  only  detailed  experimental  studies  of  the  life  history  of  the 
San  Jose  scale  hitherto  published  are  those  of  Theodore  A.  Pergande, 
in  Howard  and  Marlatt's  comprehensive  discussion  of  this  insect, 
which  appeared  in  1896.*  According  to  this  report,  four  complete 
generations  of  the  San  Jose  scale  were  regularly  bred  at  Washing- 
ton, with  the  possibility  of  a  partial  fifth  generation,  and  the  astound- 
ing total  of  3,216,080,400  was  given  as  the  possible  number  of  de- 
scendants from  a  single  female  in  a  single  season. 

Noticing  that  in  these  breeding  experiments  no  account  was  taken 
of  the  difference  in  the  number  of  annual  generations,  and  conse- 
quently in  the  number  of  descendants  produced  by  the  first-born  of 
the  first-born  of  each  generation,  and  by  the  last-born  of  the  last- 
born  of  the  same  series — a  consideration  to  which  attention  was 
called  by  the  writer  in  1906 1 — it  was  thought  best  to  duplicate  these 
studies  at  Urbana  by  methods  which  would  bring  this  factor  into 
view ;  and  the  problem  was  assigned  to  Mr.  West  for  solution  in  1908. 

Young  and  vigorous  trees  of  the  Ben  Davis  variety,  on  which 
the  insect  multiplies  freely,  were  selected  for  the  purpose ;  and  glass 
rings  10  mm.  in  height  and  35  mm.  in  interior  diameter  were  fixed 
on  the  tree  by  means  of  paraffin  or  wax.  Into  one  of  these  cylinders 
were  put  crawling  young  which  were  to  start  a  new  generation.  The 
ring  was  covered  either  with  a  band  of  closely  woven  muslin  or  with 
glass.  Cylinders  with  glass  covers  were  not  satisfactory,  however,  if 
so  placed  as  to  receive  the  direct  rays  of  the  summer  sun,  and  the 
cells  were  almost  invariably  placed  on  a  shaded  part  of  the  tree.  It 
was  our  plan  to  rear  two  series  of  generations,  starting  in  each  case 
with  the  first  and  the  last  young  of  each  brood  of  the  insects.  By 
taking  the  first-born  of  each  brood,  the  generations  were  brought  as 
close  together  as  possible,  giving  the  maximum  number  for  the  sea- 
son. By  taking  the  last-born  of  each  brood,  the  generations  were 
separated  as  widely  as  possible,  giving  the  minimum  number  for  a 
season. 


•Bull.  3,  N.  S.,  Div.  Ent.,  U.  S.  Dept.  Agr.,  p.  43. 

tThe  Corn  Root-aphis  and  its  Attendant  Ant.     Bull.  60,  Bur.  Ent.,  U.  S. 
Dept.  Agr.,  1906,  p.  31. 


1915} 


ON  THE  SAN  JOSE  SCALE 


547 


Two  hibernating  females  found  producing  young  on  May  30 
(the  first  larvse  of  the  season  to  appear)  were  surrounded  by  cells 
as  above  described,  and  several  of  the  first  young  born  from  them 
were  carefully  transferred  on  a  camel's  hair  brush  to  similar  cells. 
In  this  manner  two  colonies  were  started  from  two  similar  parents ; 
and  they  were  carried  thru  the  season,  with  a  break,  however,  in  one 
of  them,  caused  by  the  melting  in  July  of  the  paraffin  which  fastened 
the  cell  to  a  limb  of  the  tree.  The  following  diagram,  devised  by 
Mr.  West,  gives  a  complete  view  of  the  generations  of  the  San  Jose 
scale  as  they  were  thus  reared  in  the  open  air  at  Urbana,  111.,  during 
the  season  of  1908.  The  oblique  lines  indicate  the  growing  period 
of  the  young  insects;  the  horizontal  lines,  the  period  of  maturity 
during  which  young  were  produced ;  and  each  bent,  but  unbroken, 
line  represents  the  entire  period  of  the  generation,  except  that  no 
account  was  taken  of  the  life  of  the  female  after  she  had  ceased  to 
reproduce.  An  x  on  the  diagram  indicates  the  point  of  origin  of 
a  generation  from  the  first-born  young  of  a  brood ;  and  a  z,  the  point 
of  origin  of  a  generation  from  the  last -born  young.  The  W  at  the 
left  indicates  a  hibernating  female  from  which  the  series  originated, 
and  the  W's  at  the  right  indicate  the  groups  of  hibernating  young 
produced. 


MAY 


JUNE 


JULY 


AUG. 


«PT. 


OCT. 


NOV. 


W 


'-W 


FIG.   1. — Diagram  of  Annual  Generations  descending  from  one  Hibernating 
Female.     Urbana  experiment. 


548  BULLETIN  No.  180  [March, 

One  of  the  two  hibernating  females,  born  the  preceding  year, 
brought  forth  109  young  between  May  30  and  July  9.  The  first- 
born of  these,  belonging  to  the  first  generation  of  the  year,  produced 
442  young  from  July  9  to  August  22.  The  first-born  of  this  second 
generation  produced  491  young  between  August  14  and  September 
28,  and  the  first-born  of  this  third  generation  brought  forth  235 
young  between  September  17  and  October  25.  The  earliest  descend- 
ants of  this  third  generation  were  but  partly  grown  when  the  winter 
came  on.  This  fourth  generation  thus  forms,  of  course,  a  part  of 
the  hibernating  group  corresponding  to  that  with  which  the  series 
started.  There  were  thus  four  generations  in  a  year  of  this  series 
of  the  first-born,  the  number  of  young  for  each  female  of  the  suc- 
cessive generations  being  109,  442,  491,  and  235  respectively — an 
average  of  319  to  the  generation.  The  last-born  of  this  hibernating 
female  appeared  July  9,  but  these  were  lost  by  the  accident  mentioned 
above. 

Turning  now  to  the  second  female  of  the  hibernating  generation, 
with  which  a  second  parallel  series  of  breedings  began,  we  find  that 
this  female  produced  between  May  30  and  July  15,  186  young  of  a 
first  generation ;  that  the  first-born  of  this  generation  brought  forth, 
between  July  12  and  August  24,  503  young  of  the  second  generation; 
that  the  earliest  born  of  these  produced,  between  August  17  and 
September  29,  528  young  of  a  third  generation;  and  that  from  the 
first-born  of  these,  262  young  of  the  fourth  or  hibernating  generation 
were  produced  between  September  19  and  October  28.  We  thus  have 
four  annual  generations  of  the  first-born  of  this  series  also,  with  186, 
503,  528,  and  262  young  in  the  successive  series — an  average  of  369 
to  the  generation. 

The  last-born  of  the  hibernating  female  with  which  this  second 
series  began  appeared  July  15,  and  the  last-born  of  the  498  young 
produced  by  this  first-generation  parent  appeared  October  1.  These 
were  not  yet  mature  when  the  winter  overtook  them,  and  they  form 
a  part,  of  course,  of  the  hibernating  group.  This  gives  us  but  two 
annual  generations  of  the  last-born  series — but  two  "complete"  gen- 
erations— and  an  average  for  the  year  of  three  generations  when  both 
first-born  and  last-born  series  are  taken  into  account. 

By  reference  to  the  diagram  it  will  be  seen  that  there  are  three 
other  lines  of  succession  intermediate  between  these  two  extremes, 
and  that  each  of  these  three  lines  represents  three  generations,  mak- 
ing a  total  of  sixteen  generations  for  the  five  lines  or  an  average, 
again,  of  three  generations  for  the  whole  group.  It  will  also  be  seen 
from  this  diagram  that  the  generations  represented  by  the  San  Jose 
scales  present  and  alive  in  each  month  were  as  follows:  May,  the 
hibernating  generation ;  June,  the  hibernating  and  first  generations ; 
July,  the  hibernating,  first,  and  second;  August,  the  first,  second, 
and  third;  September,  the  first,  second  and  third,  and  the  fourth, 


1015]  ON  THE  SAN  JOSE  SCALE  549 

which  is  part  of  the  hibernating  generation  to  continue  into  the  follow- 
ing year ;  and  October,  the  second,  third,  and  fourth.  The  hibernating 
assemblage  contains  representatives  of  at  least  three  generations — the 
second,  third,  and  fourth  of  the  season — and  these  are  of  all  ages,  from 
young  just  fixed  to  those  adult  and  quite  ready  to  reproduce,  or  per- 
haps with  a  part  or  all  of  their  brood  already  brought  forth. 

A  comparison  of  the  intervals  between  birth  and  maturity  shows, 
as  might  have  been  expected,  shorter  growth  periods  with  the  ad- 
vancement of  the  season,  those  of  three  successive  generations  of  the 
descendants  of  the  first  overwintering  female  being  40,  37,  and  34 
days  respectively,  and  those  of  the  second  overwintering  female  be- 
ing 43,  37,  and  33  days.  The  reproductive  periods  of  the  successive 
generations  differ  little  in  length,  but  widely  in  productivity,  the 
June  and  October  generations  containing  fewer  young  than  those 
brought  forth  in  July,  August,  and  September.  The  October  young, 
indeed,  were  all  produced  during  intervals  of  warm  weather  between 
periods  of  heavy  frost. 

Evidently  there  can  be  no  computation  worth  making  of  the 
actual  or  possible  rate  of  multiplication  of  the  San  Jose  scale  which 
does  not  take  account  of  the  facts  here  given  concerning  the  maximum 
and  minimum  numbers  of  the  generations  of  the  annual  cycle,  as 
shown  by  the  first-born  and  the  last-born  series  respectively,  together 
with  the  proportion  of  each  generation  which  are  males  and  of  the 
various  rates  of  multiplication  in  different  parts  of  the  season.  On 
the  basis  of  the  above  data  of  West's  experiment,  together  with  Per- 
gande's  percentages  of  males  and  females  for  the  different  genera- 
tions, P.  A.  Glenn,  of  my  office  staff,  has  worked  out  a  day  by  day 
computation  of  births  and  deaths  of  both  males  and  females  for  the 
period  of  152  days  during  which  reproduction  was  in  progress  at 
Urbana,  with  the  result  that  there  would  have  been  produced  by 
October  28,  under  ideal,  optimum  conditions,  32,791,472  descendants 
of  a  single  female  of  the  hibernating  generation,  of  which  32,440,025 
would  have  been  still  alive,  49.4  percent  would  have  been  a  week 
old  or  less,  27.6  percent  between  one  and  two  weeks  old,  13.6  percent 
between  two  and  three  weeks,  5.5  percent  between  three  and  four 
weeks,  and  1.11  percent  more  between  four  and  five  weeks  old,  and 
only  2  percent  would  have  been  mature. 

I  am  assuming  that,  as  the  average  growth  period  at  Urbana  was  37 
days,  each  week  after  birth  would  add  about  one  fifth  of  the  growth  to 
adult  size.  The  import  of  these  figures  may  be  better  realized  if  they  are 
expressed  in  the  area  which  the  total  number  of  scales  present  in 
their  various  sizes  October  28  would  cover  if  placed  in  a  single  layer 
edge  to  edge.  The  average  diameter  of  an  equal  number  of  male  and 
female  scales  is  1.1  mm.  Taking  this  at  1  mm.  and  making  propor- 
tionate allowance  for  the  lesser  size  of  the  scales  at  the  various  stages 
of  growth,  we  find  that  the  entire  product  of  reproduction  alive  Octo- 


550  BULLETIN  No.  180  [March, 

ber  28  is  equivalent  to  8,803,283  adult  scales — a  number  sufficient 
to  cover  94.8  square  feet. 

Even  this  estimate  of  a  possible  product  of  multiplication  must 
be  regarded  as  excessive  if  we  take  note  of  the  fact,  reported  by 
Lowe  and  Parrott,  of  New  York,*  that  an  average  of  nearly  40  per- 
cent of  the  young  scales  may  perish,  apparently  from  mere  physi- 
ological causes,  without  settling  down  to  feed  and  secrete  the  pro- 
tecting scale.  In  Mr.  West's  studies  no  attempt  was  made  to  trace 
the  fate  of  any  of  the  young  except  those  chosen  as  parents  of  the 
generation  to  follow. 

These  data  of  the  Urbana  experiment,  obtained  from  a  repro- 
duction season  beginning  May  30  and  closing  October  28,  no  doubt 
give  us,  however,  a  product  very  much  smaller  than  might  be  worked 
out  for  southern  Illinois,  and  probably  a  larger  product  than  the 
northern  Illinois  normal  rate  of  increase.  More  than  75  percent  of 
the  entire  theoretical  product  of  the  season  was  but  two  weeks  old 
or  less  October  28,  and  8  percent  of  the  scale  insects  alive  at  that 
date  would  have  been  but  one  day  old.  A  relatively  slight  lengthen- 
ing of  the  period  of  reproduction  would  evidently  have  added  enor- 
mously to  the  total  number  produced,  f  At  Alton,  crawling  young 
were  seen,  in  1908,  up  to  November  9,  and  in  1906  newly  born  young 
were  found  by  E.  D.  Glasgow,  in  Williamson  county,  January  4.  It 
is  certain  that  young  fruit-trees  are  much  more  rapidly  destroyed 
in  southern  Illinois  by  San  Jose  scale  than  in  the  northern  part  of 
the  state,  and  that  the  scale  spreads  more  rapidly  there  and  is  more 
difficult  to  keep  in  check;  and  our  experience  also  shows  that  in- 
festation by  this  insect  is  decidedly  more  injurious  to  susceptible 
plants  in  southern  Illinois  than  it  is  in  the  central  part  of  the  state. 

TESTS  OF  ORCHARD  SPRAYS 

Comparative  tests  of  orchard  sprays  for  the  San  Jose  scale  have 
been  many  times  made,  with  the  general  result  that  the  modern  lime- 
sulphur  preparations  have  come  into  very  general  use;  and  they 
seem  likely  to  maintain  this  lead  particularly  by  reason  of  a  special 
value  as  fungicides  which  gives  them  an  advantage  over  the  petroleum 
preparations,  their  only  real  competitors.  Nevertheless,  careful  ex- 
periments made  by  the  office  force  of  the  State  Entomologist  from 
1907  to  1911  seem  still  worthy  of  report,  at  least  as  a  part  of  the 
permanent  record. 

It  was  the  principal  purpose  of  these  experiments,  which,  be- 
ginning in  the  fall  of  1907,  were  planned  to  continue  for  five  years 
upon  the  same  orchards,  to  learn  whether  it  was  possible  to  redeem 

*Bull.   193,  N.  Y.  State  Agr.  Exper.  Sta.,  Dec.,  1900,  p.  355. 

tin  another  paper  of  this  report,  this  fact  is  taken  into  account  in  a  compu- 
tation of  the  product  of  periods  ten  days  shorter  and  ten  days  longer  than  the 
above. 


1915}  QN  THE  SAN  JOSE  SCALE  SSI 

orchards,  already  considerably  or  badly  infested  and  situated  in  a 
generally  infested  territory,  by  measures  which  would  make  this 
economically  worth  while;  and  at  the  same  time  to  show  which  of 
the  various  treatments  used  was  the  most  successful  and  the  most 
profitable.  This  purpose  was  in  part  defeated,  however,  by  the  failure 
of  a  company  with  which  our  contract  for  insecticide  supplies  was 
made  to  deliver  the  materials  ordered  in  time  for  use  in  1910.  A 
breakdown  in  their  factory  of  which  we  were  not  notified  until  it 
was  too  late  to  obtain  supplies  from  another  source,  prevented  our 
spraying  these  orchards  in  that  year,  and  the  San  Jose  scale  conse- 
quently multiplied  for  a  season  without  restraint.  These  orchards 
were  saved  notwithstanding,  and  are  now  in  profitable  use,  but  at  a 
heavier  loss  and  a  greater  expense  than  was  necessary. 

EXPERIMENTS  OF  1907-08 

Two  apple  orchards,  originally  of  1200  and  1600  trees  respect- 
ively, belonging  to  James  M.  Etherton  and  Homer  Etherton,  and 
situated  about  eight  miles  south  of  Murphysboro,  Jackson  county,  in 
southern  Illinois,  were  selected  for  these  tests.  Both  contained  Ben 
Davis  and  Winesap  apple-trees,  so  set  in  the  spring  of  1903  with 
two-year-old  nursery  stock  that  the  orchards  could  be  readily  divided 
into  similar  experimental  plots  of  sufficiently  large  size  to  permit  the 
omission  of  the  marginal  rows  of  the  plots  and  the  use,  for  compara- 
tive purposes,  of  the  central  rows  only.  This,  as  will  be  shown,  is 
an  essential  point  in  experiments  of  this  description,  since  check  and 
experimental  plots  placed  side  by  side  influence  each  other  in  a  way 
to  diminish  the  infestation  of  the  margins  of  the  former  and  to  in- 
crease those  of  the  latter. 

Infestation  data  were  obtained  by  a  critical  inspection  and  grad- 
ing as  described  in  an  earlier  article  on  "Comparative  Experiments 
with  Various  Insecticides  for  the  San  Jose  Scale,"  published  in  the 
Twenty-fourth  Eeport  of  this  office,  pages  59-77. 

GRADING  OF  THE  TREES 

The  trees  in  the  experimental  orchards  were  carefully  examined, 
one  by  one,  November  11  and  12,  1907,  by  W.  P.  Flint  and  L.  M. 
Smith,  of  the  State  Entomologist's  staff,  under  the  general  super- 
vision of  Mr.  West.  These  inspectors  worked  together  until  it  was 
evident  that  their  procedure  was  uniform,  after  which  they  worked 
separately.  The  trees  were  graded  on  a  scale  of  10  degrees,  the  sev- 
eral grades  having  the  following  significance: — 

1  signifies  a  tree  infested  by  a  trace  of  the  San  Jose  scale — so 
very  slightly  infested  that  one  must  search  to  discover  the  insects; 
2,  a  tree  slightly  infested, — that  is,  having  scattered  scales  upon  it, 
nowhere  clustered  and  yet  fairly  numerous;  3,  a  tree  slightly  in- 


552  BULLETIN  No.  180    m  [March, 

f ested,  with  the  insects  showing  a  tendency  in  places  to  form  clusters ; 
4,  a  tree  with  scales  which  show  a  decided  tendency  towards  the  for- 
mation of  clusters,  yet  have  parts  but  slightly  infested;  5,  a  mod- 
erately infested  tree,  the  scales  being  fairly  abundant  over  the  entire 
tree,  and  frequently  forming  groups  or  clusters;  6,  a  tree  mostly 
moderately  infested,  but  with  some  parts  so  badly  infested  as  to  be 
evidently  suffering;  7,  a  tree  considerable  parts  of  which  are  badly 
infested,  yet  having  parts  infested  to  only  a  moderate  degree;  8,  a 
tree  for  the  most  part  badly  infested,  but  not  incrusted,  evidently 
suffering  from  the  attack  of  the  scale ;  9,  a  tree  badly  infested,  with 
some  parts  incrusted;  and  10,  an  incrusted  tree.  Cases  where  the 
scale  was  peculiarly  distributed  on  a  tree,  making  its  classification 
difficult,  were  decided  by  consultation.  I  am  told,  however,  by  the 
inspectors  grading  these  trees,  that,  in  practice,  the  grades  between 
1  and  10  were  essentially  estimates  of  the  relative  parts  of  the  sur- 
face of  the  tree  occupied  by  the  scales,  a  grade  of  four,  for  example, 
indicating  that  twice  as  much  surface  was  infested  as  in  grade  2, 
and  so  on.  It  was  found  that  the  trees  could  be  readily  graded,  for 
the  most  part,  on  this  scale  and  that  the  two  men  working  inde- 
pendently would  agree  almost  exactly  in  their  estimate  of  the  inten- 
sity of  the  infestation.  The  orchard  containing  originally  1200  trees 
was  generally  and  badly  infested,  while  the  other,  containing  originally 
1600  trees,  was  infested  much  more  moderately. 

THE  EXPERIMENTAL  PLOTS 

Four  insecticides  were  tested  in  this  year's  operations  in  a  way 
to  compare  for  each  the  relative  effects  of  a  single  fall  application, 
a  single  spring  application,  and  two  applications,  one  in  fall  and 
the  other  in  spring.  The  more  heavily  infested  orchard  (No.  I), 
showing  an  average  infestation  of  7.4  degrees,  was  divided  into  five 
plots,  one  of  which  was  reserved  as  a  check,  and  the  remaining  four 
were  treated  fall  and  spring  with  the  four  insecticides.  The  check 
plot  was  six  rows  wide,  plots  2  and  3  were  fourteen  rows  wide,  and 
plots  4  and  5,  thirteen  rows.  Orchard  No.  II,  the  infestation  of 
which  averaged  3.9  degrees,  was  divided  into  nine  plots,  one  of  which 
was  reserved  as  a  check,  the  remainder  being  used  to  test  the  effect 
of  a  single  application  of  each  of  the  four  insecticides  in  fall  and  in 
spring.  These  plots  were  six  rows  wide,  except  the  one  nearest  the 
check  (7),  which  was  made  ten  rows  wide  in  order  that  a  more  liberal 
allowance  might  be  made  for  the  influence  of  the  check  plot  upon  the 
experimental  plot  adjoining  than  for  the  effects  of  adjacent  experi- 
mental plots  upon  each  other. 

INSECTICIDES 

The  lime-sulphur  mixture  applied  was  the  15,  15,  50  preparation 
in  general  use  by  us  in  1908.  Fifteen  pounds  each  of  sulphur  and 


1915]  ON  THE  SAN  JOSE  SCALE  553 

fresh  stone-lime  were  boiled  together  for  forty-five  minutes,  to  make 
a  strong  solution,  and  this  was  then  diluted  with  cold  water  to  make 
fifty  gallons.  This  "home-made"  was  compared  with  the  "Rex" 
lime-sulphur  solution  of  the  Rex  Company,  of  Nebraska,  one  part 
of  which  was  used  with  eleven  parts  of  water ;  with  Scalecide,  made 
by  the  B.  G.  Pratt  Company,  of  New  York,  one  part  to  twenty  of 
water;  and  with  the  Target  Brand  Scale  Destroyer  made  by  the 
American  Horticulture  Distributing  Co.,  of  West  Virginia,  one  part 
to  twenty  of  water. 

These  insecticides  were  applied  with  an  Eclipse  No.  6  pump 
carrying  two  leads  of  hose  and  10-foot  extension-rods.  Each  of  the 
extension-rods  was  provided  with  a  double  Vermorel  nozzle.  The 
spray  barrel  was  thoroly  cleansed  when  the  change  was  made  from 
one  insecticide  to  another.  New  nozzle  caps  having  an  aperture  of 
about  three-fourths  mm.  diameter  were  used,  caps  showing  any  wear 
being  discarded.  A  constant  strong  pressure  was  maintained  on  the 
pump  so  that  the  spray  was  finely  divided,  "singing"  as  it  left  the 
nozzle.  The  various  insecticides  were  applied  in  as  thoro,  uniform, 
and  fair  a  way  as  possible. 

In  Orchard  No.  I  the  home-made  lime-sulphur  wash  and  the  Rex 
lime-sulphur  solution  were  applied  to  plots  2  and  3,  November  19, 
1907 ;  the  Target  Brand  and  Scalecide  on  plots  4  and  5,  November 
23.  The  same  plots  were  treated  in  the  same  way  a  second  time 
March  11  and  12,  1908.  Plots  7  to  10  inclusive,  of  Orchard  No.  II, 
were  sprayed  November  24,  1907,  and  plots  11  to  14  inclusive  were 
sprayed  March  12  and  13,  1908. 

FINAL  GRADING 

October  5,  1908,  all  the  trees  in  these  orchards  were  graded  a 
second  time  by  Mr.  Flint  and  Mr.  Smith.  Mr.  Smith  knew  nothing 
of  the  details  of  the  experiment.  Altho  Mr.  Flint  assisted  in  spraying 
the  trees  in  November,  1907,  he  was  not  in  the  orchards  again  until 
the  final  grading  of  the  trees,  and  the  stakes  which  marked  the  plots 
had  in  the  meantime  been  removed. 

Results  of  Treatment. — The  results  of  a  spraying  operation  may 
be  stated  in  a  way  to  compare  the  condition  of  the  experimental  plot 
at  the  time  of  spraying  with  its. condition  after  the  lapse  of  a  season 
has  made  it  possible  to  spray  again.  The  ratio  of  these  two  stages 
of  infestation,  the  original  and  the  final  stage,  I  have  called  the  ratio 
of  improvement  or  the  ratio  of  loss  or  gain.  If  there  is  a  check  plot 
in  the  series,  the  rate  of  progress  of  its  infestation  during  the  season 
may  be  used  to  show  the  stage  of  infestation  which  the  experimental 
plot  would  have  reached  if  no  spraying  had  been  done,  and  the 
original  infestation  of  this  plot  may  be  compared  with  this  theoretical 
final  stage,  so  ascertained.  The  ratio  of  these  two  stages  I  have 


554 


BULLETIN  No.  180 


[March, 


called  the  ratio  of  benefit.*    In  the  following  table  both  these  ratios 
are  shown  for  Orchard  II,  but  the  ratios  of  benefit  are  not  given  for 

ETHERTON  ORCHARDS,   1907-08 
ORCHARD  I 


Plot 

Trees 
exam- 
ined 

Treatment 

Date 

In- 
festa- 
tion 
1907 

In- 
festa- 
tion 
1908 

Loss 
(—  ),or 
gain 
(+) 

Perct. 
of  loss 
or 
gain 

Per  ct. 
of 
benefit 

1 

64 

None   (check) 

6.265 

8.323 

—2.058 

—32.9 

2 

148 

Lime-Sulphur 
15  L.,  15  S.,  50  W. 

Nov.  19 
March  11 

8.4 

5.8 

+2.6 

+31. 

3 

149 

Rex  Lime-Sulphur, 
1  part;    water,  11 

Nov.  19 
March  11 

8.8 

5.95 

+2.85 

+34.4 

4 

222 

Target  Brand, 
1  part;    water,  20 

Nov.  23 
March  11 

7.6 

6.1 

+1.5 

+20. 

5 

181 

Scalecide, 
1  part;    water,  20 

Nov.  23 
March  12 

5.9 

4.2 

+1.7 

+28.8 

ORCHARD  II 


6 

86 

None   (check) 

3.44 

4.56 

—1.12 

—32.5 

7 

109 

Lime-Sulphur 
15  L.,  15  S.,  50  W. 

Nov.  24 

4.33 

2.65 

+1.68 

+38.4 

53.8 

8 

108 

Eex  Lime-Sulphur, 
1  part;    water,  11 

Nov.  24 

4.04 

2.65 

+1.39 

+40.4 

50.6 

9 

92 

Target  Brand, 
1  part;    water,  20 

Nov.  24 

5.37 

3.66 

+1.71 

+31. 

48.6 

10 

111 

Scalecide, 
1  part;    water,  20 

Nov.  24 

4.88 

3.02 

+1.86  " 

+38. 

53.3 

11 

101 

Lime-Sulphur 
15  L.,  15  S.,  50  W. 

March  12 

4.09 

2.11 

+1.98 

+48.4 

61.1 

12 

104 

Rex  Lime-Sulphur, 
1  part;    water,  11 

March  13 

3.1 

1.58 

+1.52 

+49. 

61.5 

13 

128 

Target  Brand, 
1  part;    water,  20 

March  13 

2.87 

1.9 

+  .97 

+33.7 

50. 

14 

115 

Scalecide, 
1  part;    water,  20 

March  13 

2.52 

1.53 

+  .99 

+39.4 

53.7 

6  —  a 


*The  following  is  a  convenient  formula  for  use  in  this  computation: 


+  c — d 


=  x;  a  being  the   degree   of  original  infestation   of   the   check 


ft  — a 

-c  +  c 

a 

plot;  6,  the  final  infestation  of  that  plot;  c,  the  original  infestation  of  the 
experimental  plot;  d,  the  final  infestation  of  the  same;  and  x,  the  ratio  of 
benefit. 


1915}  ON  THE  SAN  JOSE  SCALE  SSS 

Orchard  I,  because  the  original  infestation  of  this  orchard  was  so 
high  that  an  increase  in  plots  2,  3,  and  4  at  the  rate  of  the  check 
plot,  would  have  completely  incrusted  these  trees  long  before  the  end 
of  the  season.  In  other  words,  this  orchard  was  too  heavily  infested 
in  the  beginning  to  be  fit  for  full  use  in  our  experimental  program. 

By  an  inspection  of  the  foregoing  table  we  find  that  two  treat- 
ments, fall  and  spring,  of  the  heavily  infested  orchard  (the  average 
infestation  of  whose  experimental  plots  was  7.67  degrees)  produced 
less  effect  than  a  single  spraying,  in  either  fall  or  spring,  of  the 
moderately  infested  orchard  (the  infestation  of  whose  experimental 
plots  averaged  3.9  degrees).  The  average  improvement  of  plots  2 
and  3  in  Orchard  I,  the  trees  in  which  were  twice  sprayed  with  lime- 
sulphur  preparations,  was  32.7  percent,  while  that  of  plots  7  and  8 
in  Orchard  II,  once  sprayed  in  fall,  was  39.4  percent,  and  that  of 
plots  11  and  12,  once  sprayed  in  spring,  was  48.7  percent.  This  fact 
illustrates  clearly  the  importance  of  early  spraying  before  infestation 
becomes  serious.  In  these  experimental  orchards  there  were  but  few 
crawling  young  up  to  August  1  on  any  of  the  treated  trees  which  had 
originally  been  infested  to  8  degrees  or  less;  while  on  trees  grading 
9  and  10  degrees,  crawling  young  were  fairly  abundant  thru  July, 
and  began  about  the  middle  of  August  to  cause  a  considerable  re- 
infestation  of  surrounding  sprayed  trees,  this  dispersal  increasing 
rapidly  as  the  season  progressed.  "While  the  insecticide  treatment 
reduced  a  few  of  the  completely  incrusted  trees  to  the  6th  degree  of 
infestation,  many  of  those  incrusted  at  the  beginning  of  the  experi- 
ment were  partially  or  completely  incrusted  again  by  the  end  of  the 
summer. 

The  records  of  the  checks  in  both  orchards  show  a  seasonal  in- 
crease amounting  to  about  one-third  of  the  original  infestation ;  while 
the  lime-sulphur  treatments  of  plots  2  and  3  in  November  and  March 
worked  a  reduction  of  about  a  third  of  the  8.5  degrees  original  in- 
festation of  these  plots.  There  was  thus  every  reason  to  believe  that 
a  continuation  of  this  program  would  save  this  orchard  and  virtually 
clear  the  trees  of  the  scale ;  and  this,  I  am  informed,  has  since  been 
done,  both  of  these  orchards  being  now  productive  and  in  good  con- 
dition. 

The  difference  in  effect  between  fall  and  spring  spraying  with 
lime-sulphur  was  shown  by  a  comparison  of  the  ratio  of  benefit  (52.2 
percent)  of  plots  7  and  8,  sprayed  in  fall,  with  those  of  plots  11  and 
12  (61.3  percent),  sprayed  in  spring — a  difference  of  about  17  per- 
cent in  favor  of  the  spring  spraying.  A  similar  comparison  of  the 
ratios  of  benefit  of  plots  10  and  14,  sprayed  with  Scalecide,  gives  us 
a  difference  of  less  than  1  percent  in  favor  of  the  spring  spraying,  and 
the  ratios  of  plots  9  and  13,  treated  with  Target  Brand,  show  a  differ- 
ence of  less  than  3  percent  in  favor  of  that  insecticide.  This  is  in 
accord  with  the  general  opinion  that  a  spring  spraying  with  lime- 


556  BULLETIN  No.  180  [March, 

sulphur  prevents  a  fixation  of  the  young  scales  more  effectually  than 
a  treatment  with  the  kerosene  sprays.  We  also  learn  from  the  fore- 
going table  that  Scalecide  was  somewhat  less  effective  than  either 
form  of  lime-sulphur  used ;  and  that,  of  the  two  latter,  Rex  dip  was 
about  5  percent  more  effective  than  the  home-made  solution. 

THE    TRANSITION    ZONE   IN    INSECTICIDE   EXPERIMENTS 

In  the  Twenty-fourth  Report  of  this  office  (1908)  I  called  par- 
ticular attention  to  a  generally  neglected  factor  in  field  experimenta- 
tion with  insecticides  and  other  means  of  insect  control;*  namely, 
the  fact  that  the  effects  of  insecticide  treatment  of  experimental  plots 
are  likely  to  be  diminished  and  disguised  by  an  invasion  of  these 
plots  by  insects  migrating  from  adjacent  untreated  parts  of  the  or- 
chard or  field;  and  in  that  paper  I  illustrated  this  influence  by  a 
comparison  of  the  degrees  of  infestation  of  check  rows  near  experi- 
mental plots  and  experimental  rows  near  check  plots  with  the  degrees 
of  infestation  of  rows  in  each  kind  of  plot  at  some  distance  from  the 
other.  The  practical  outcome  of  this  comparison  was  a  general  rule 
that  large  enough  plots  should  always  be  made  in  field  experiments 
to  give  interior  parts  freedom  from  the  influence  of  one  plot  upon 
another,  and  that  the  marginal  parts  of  the  plots  should  not  be  used 
in  assembling  data  for  comparison. 

This  principle  is  amply  illustrated  in  the  results  of  the  orchard 
experiments  now  under  discussion.  The  check  rows  next  the  experi- 
mental plots  were  less  infested  by  San  Jose  scale  at  the  end  of  the 
season,  and  the  experimental  rows  nearest  the  check  plots  were  more 
infested,  than  were  those  at  some  distance  from  the  line  of  division. 
This  mutual  influence  of  one  plot  upon  the  other  varied  somewhat 
with  the  degree  of  infestation,  the  neutral  or  transition  zone  of  un- 
available trees  being  five  rows  wide  in  the  less-infested  orchard  and 
six  rows  wide  in  that  more  infested.  This  transition  zone  was  due, 
of  course,  to  the  movement  of  the  young  insects  across  the  boundary 
between  the  plots,  the  marginal  rows  of  the  check  losing  more  than 
they  received  from  the  experimental  plot  adjoining,  and  the  experi- 
mental plot  reversing  the  process.  Even  the  outside  rows  of  the  check 
plot  show,  as  might  be  expected,  the  same  loss  of  infesting  insects,  so 
that  only  three  rows  were  left  available  for  use  in  a  check  plot  six  rows 
wide. 

The  detailed  data  are  given  in  the  accompanying  diagrams,  one 
representing  the  less-infested  orchard  and  the  other  the  more-infested. 
The  vertical  lines  on  each  diagram  stand  for  the  orchard  rows  in  two 
adjacent  plots,  one  the  check  and  the  other  sprayed  with  home-made 
lime-sulphur  wash.  The  heavy  line  between  rows  6  and  7  is  the 

*' '  Spraying  Apples  for  the  Plum-'curculio, ' '  pp.  94-99. 


1915] 


ON  THE  SAN  JOSE  SCALE 


557 


dividing  line  between  these  two  plots,  and  the  heavy  horizontal  line 
marked  with  a  zero  stands  for  the  average  infestation  of  these  plots 
before  the  spraying  was  done.  The  plus-figures  at  the  left  of  each 
diagram  indicate  degrees  of  increase  in  the  infestation  of  the  check 
plot  during  the  season  following,  and  the  minus-figures  denote  degrees 
of  decrease  of  the  infestation  at  the  end  of  the  season  as  a  conse- 
quence of  the  treatment  received.  The  broken  line  running  diagonally 
across  the  diagram  is  drawn  in  a  way  to  show,  at  the  point  where 


Gain 
r  "~ 

Check  Wot  (ro*s) 

Exjberifnenfcit  Ptot  (rows) 

-4 
-3 
-2 
-/ 
0 
+1 
+2 
+3 

• 

-M 

7aT~~- 

tat 

t-8S 

l£4 

MS 

1S3 

/ 

<f 

/ 

'J7 

PS 

tx 

^ 

IX. 
J6 

Zf 

ZJ      - 

FIG.  2. — Diagram  showing  Transition  Zone,  Orchard  I,  between  Check  Plot 
and   Experimental  Plot,  Lime  and  Sulphur  Treatment. 


Gain 
Loss 


+  2 


CAecJtr  Wot. 


J.66 


10  //  12  JS 


FIG.  3. — Diagram  showing  Transition  Zone,  Orchard  II,  between  Check  Plot 
and  Experimental   Plot,  Lime  and   Sulphur   Treatment. 


558  BULLETIN  No.  180  [March, 

it  crosses  a  vertical,  the  degree  of  loss  or  gain  for  that  row,  and  the 
figures  on  the  face  of  the  diagram  give  those  degrees  precisely.  It 
will  be  readily  understood  that  if  the  check  plot  and  the  experimental 
plot  were  without  influence  one  upon  the  other — if  there  had  been 
no  movement,  that  is  to  say,  of  the  San  Jose  scale  across  the  dividing 
line  between  the  plots — then  both  these  transverse  lines  on  the  dia- 
gram would  have  been  virtually  horizontal,  their  inner  ends  as  widely 
separated  in  a  vertical  direction  as  are  their  outer  ends,  substantially 
as  shown  by  the  transverse  dotted  lines.  The  oblique  part  of  each 
line  marks  the  transition  zone;  and  the  upward  turn  of  both  lines 
at  the  left  is  an  indication  of  the  loss  of  insects  from  the  outside  rows 
of  the  check  plots. 

EXPERIMENTS  OF  1909 

Continuing  our  operations  in  the  Etherton  orchards  in  1909,  we 
used  for  spraying  experiments  only  Orchard  II.  Orchard  I  received 
a  single  spraying,  for  the  mere  control  of  the  scale,  March  18-23, 
1909,  with  home-made  lime-sulphur  prepared  as  in  the  preceding 
year.  According  to  the  grading  of  October,  1908,  the  infestation  of 
this  orchard  taken  as  a  whole  averaged  5  degrees  on  a  scale  of  10, 
and  when  graded  again  in  January,  1910,  its  average  was  2.39  de- 
grees, a  gain  in  condition  of  52.2  percent  within  the  year  as  the  result 
of  the  treatment. 

Orchard  II  was  carefully  graded  March  11,  1909,  and  was  di- 
vided into  four  plots.  One  was  reserved  as  a  check  and  the  other 
three  were  sprayed,  respectively,  with  home-made  lime-sulphur,  lime 
and  sulphur  manufactured  by  the  Grasselli  Company,  and  a  petro- 
leum preparation  known  to  the  trade  as  San-U-Zay  Scale  Oil.  The 
experimental  plots  were  sprayed  March  23-25  by  Mr.  L.  M.  Smith, 
assisted  by  one  man  and  two  boys,  all  entirely  inexperienced  in  such 
work.  Rains  fell  every  day  during  the  spraying,  and  showers  and 
high  winds  on  the  24th  made  the  work  "very  unsatisfactory."  Prob- 
ably on  this  account,  and  because  of  the  inexperience  of  the  operators, 
the  results  of  these  experiments  were  much  less  favorable  than  those 
of  the  preceding  and  succeeding  years.  A  second  grading,  for  a 
comparison  of  conditions  and  an  analysis  of  results,  was  made  Janu- 
ary 17-18,  1910.  From  the  following  table  it  will  be  seen  that  the 
three  preparations  used  were  in  practically  the  same  class  as  to 
results  produced,  the  home-made  lime-sulphur,  however,  falling  a 
little  short  of  the  other  two.  It  was  an  interesting  fact  that  the 
"miscible  oil"  preparation  applied  in  March  seemed  practically  equal 
in  value  to  the  solutions  of  lime  and  sulphur. 


1915} 


ON  THE  SAN  JOSE  SCALE 


559 


ETHERTON  ORCHARD  EXPERIMENT,  1909 
ORCHARD  II 


No. 
of 
plot 

No. 
of 
trees 

Treatment 

Date 

Average 
infestation 

Per  ct. 
of  loss 
or  gain 

Per  ct. 
of 
bene- 
nt 

March 
1909 

Jan. 

1910 

1 

93 

None    (check) 

4.81 

5.57 

—15.8 

2 

50 

Lime-Sulphur 
Grasselli  Chem.  Co. 

March  25 

5.56 

4.93 

+11.3 

23.4 

3 

190 

Lime-Sulphur 
home-made 

March  23-26 

3.17 

2.96 

+  6.6 

19.3 

4 

94 

San-TJ-Zay  Scale  Oil 

March  25 

3.09 

2.77 

+10.3 

22.6 

EXPERIMENTS  OP  1911 

After  the  omission  of  1910,  due  to  the  failure  of  the  insecticide 
company  to  fill  our  orders  on  time,  both  of  the  Etherton  orchards 
were  taken  in  hand  in  1911  for  experimental  work.  Orchard  II  was 
divided  into  four  plots,  which  were  sprayed,  February  27  to  March 
6,  with  different  brands  of  lime-sulphur.  Orchard  I  was  divided  into 
five  plots,  four  of  which  were  sprayed  March  6-9  with  different  lime- 
sulphur  preparations,  and  the  fifth  with  Scalecide.  All  the  brands 
of  manufactured  insecticides  were  bought  in  the  open  market. 

The  manufactured  lime-sulphur  solutions  were  all  mixed  with 
water  at  the  rate  of  1  gallon  to  9.  The  home-made  lime-sulphur 
contained  100  pounds  of  sulphur  and  50  pounds  of  lime  to  60  gallons 
of  water,  9  gallons  of  this  concentrate  being  diluted  with  cold  water 
to  make  50  gallons.  Otherwise  stated,  the  formula  for  this  propor- 
tion was  sulphur,  15,  lime,  iy2,  water,  50,  differing  from  the  home- 
made solution  of  the  earlier  experiments  only  in  the  smaller  pro- 
portion of  lime.  The  Scalecide  was  diluted  in  a  ratio  of  1  to  15. 

Owing  to  the  condition  of  these  orchards  because  of  a  lack  of 
treatment  the  preceding  year,  it  was  not  thought  advisable  or  safe  to 
leave  any  part  without  treatment,  and  no  check  plots  were  reserved. 
The  work  was  in  charge  of  Mr.  Flint,  assisted  by  Mr.  Smith. 

The  original  grading  was  done  by  Flint  and  Smith,  February 
22,  1911,  and  the  final  grading,  December  12  of  the  same  year.  In 
the  absence  of  checks,  only  " ratios  of  improvement"  could  be  com- 
puted. The  home-made  lime-sulphur,  poured  off  after  the  settlement 
of  suspended  matter,  gave  an  improvement  of  40  percent,  and  the 
lime-sulphur  of  the  Grasselli  Company,  38.3  percent  in  Orchard  I 
and  32.7  percent  in  Orchard  II,  while  the  Rex  lime-sulphur  treat- 
ment resulted  in  an  average  improvement  of  39.4  percent. 


560 


BULLETIN  No.  180 


[March, 


ETHEETON  ORCHARD  EXPERIMENT,  1911 
ORCHARD  I   (AVERAGE  ORIGINAL  INFESTATION,  5.84) 


No.of 
plot 

No.of 
trees 

Treatment 

Date 

Average  infestation 

Per  ct.  of 
gain 

Feb.  1911 

Dec.  1911 

1 

183 

Lime-  Sulphur 
Thomsen  Chemical  Co. 

March  6  &  7 

5.58 

4.19 

25. 

2 

185 

Lime-Sulphur 
Grasselli  Chem.  Co. 

March  7 

7.45 

4.59 

38.3 

3 

59 

Lime-Sulphur,  home- 
made, with  sludge 

March  9 

6.00 

3.70 

38.3 

4 

132 

Lime-Sulphur,  home- 
made, without  sludge 

March  8 

3.33 

2.00 

40. 

5 

144 

Scalecide 

March  8 

6.86 

5.04 

26.5 

ORCHARD  II   (AVERAGE  ORIGINAL  INFESTATION,  7.53) 


6 

142 

Lime-Sulphur 
Thomsen  Chemical  Co. 

March  4  &  6 

5.73 

2.57 

26.7 

7 

151 

Lime-Sulphur 
Grasselli  Chem.  Co. 

March  3  &  4 

8.48 

5.71 

32.7 

8 

140 

Lime-Sulphur 
Sherwin-Williams  Co. 

March  3 

7.73 

5.93 

23.2 

9 

89 

Lime-Sulphur 
Eex  Co. 

Feb.  27  & 
Mar.  2 

8.20 

4.97 

39.4 

At  the  first  glance,  it  would  seem  that  suspended  sediments  in 
the  home-made  lime-sulphur  were  disadvantageous  to  it,  the  treat- 
ment of  plot  4  with  a  clear  solution  giving  a  higher  gain  than  that 
of  plot  3  with  a  solution  whose  sediments  were  thoroly  stirred  up 
just  before  spraying.  Since  it  so  happened,  however,  that  the  origi- 
nal infestation  of  plot  4  (3.33  degrees)  was  only  a  little  more  than 
half  that  of  plot  3  (6  degrees),  it  is  altogether  likely  that  this  was 
the  cause  of  the  greater  benefit  to  plot  4. 

Obvious  differences  may  be  noted  in  the  results  of  the  treatment 
with  the  several  kinds  of  lime-sulphur  tested,  the  Thomsen  and  the 
Sherwin-Williams'  preparations  of  1911  being  apparently  in  a  differ- 
ent class  from  the  Rex,  the  Grasselli,  and  the  home-made  preparations. 

Comparing  the  data  of  this  table  with  those  for  1907  and  1908, 
we  find  fairly  similar  results  so  far  as  the  experiments  themselves 
are  fairly  comparable.  Scalecide,  for  example,  gave  us  28.8  percent 
of  gain  in  Orchard  I  in  1907,  and  26.5  percent  in  1911.  Rex  lime- 


1915]  ON  THE  SAN  JOSE  SCALE  561 

sulphur  shows  34.4  gain  for  Orchard  I  in  1907,  on  a  plot  the  original 
infestation  of  which  was  8.8  degrees,  and  a  gain  of  39.4  percent  in 
Orchard  II  in  1911  on  a  plot  the  original  infestation  of  which  was 
8.2  degrees.  It  is  true  that  the  Rex  plots  in  Orchard  II  agree  less 
closely  in  the  two  years,  the  39.4  percent  of  1911  being  matched  by 
a  gain  of  49  percent  in  1907 ;  but  a  glance  at  the  grades  of  infesta- 
tion explains  the  discrepancy,  the  1907  plot  having  an  average  grade 
before  treatment  of  3.1  degrees,  and  the  1911  plot  a  grade  of  8.20 
degrees.  We  get  a  more  obvious  improvement,  as  a  general  rule, 
where  the  average  infestation  is  the  less. 

SUMMARY 

1.  Experiments  with  infested  ripe  apples  show  that  the  San 
Jose  scale  may  live  and  reproduce  freely  on  such  fruits  plucked  from 
the  tree  and  kept  at  ordinary  room  temperatures,  and  that  living 
young  may  continue  to  be  born  under  such  conditions  during  a  period 
of  eight  weeks.    Infested  apples  taken  from  cold  storage  in  December 
gave  similar  results,  young  being  produced  on  these  apples  for  twenty- 
five  days. 

2.  Exact  breeding  experiments  conducted  at  Urbana  in  1906,  in 
a  way  to  distinguish  thruout  the  season  the  descendants  of  the  first- 
born from  those  of  the  last-born  of  each  generation,  gave  two  suc- 
cessive generations  of  the  last-born  series,  in  the  complete  year,  and 
four  such  generations  of  the  first-born  series.    A  computation  based 
on  data  thus  obtained  yielded  a  possible  rate  of  multiplication  under 
optimum  conditions  of  32,791,472  to  1  for  the  year.     This  total  is 
only  the  98th  part  of  that  of  other  investigators,  who  took  no  ac- 
count of  diminished  numbers  of  generations  produced  by  late-born 
individuals. 

3.  Spraying  operations  with  various  preparations  of  lime  and 
sulphur  and  with  two  brands  of  miscible  oils  justify  the  usual  pref- 
erence for  the  sulphur  solutions,  especially  because  of  their  more 
prolonged  effect  when  applied  in  spring.     The  home-made  solutions 
were  equally  effective  with  those  ready-made  and  requiring  only 
dilution  for  use.    These  experiments  also  illustrate  the  great  advan- 
tage of  early  spraying,  before  an  orchard  becomes  heavily  infested, 
and  furnish  evidence  that  spraying  in  spring  is  much  more  effective 
than  spraying  in  fall,  the  ratios  of  benefit  being  some  20  percent 
greater.    The  possibility  of  redeeming  and  restoring  a  badly  infested 
orchard  and  maintaining  it  in  good  condition,  with  one  or  two  spray- 
ings a  year,  was  well  established  by  these  operations. 


^  •,*»«.. 

,v 


UNIVERSITY  OF  ILLINOIS-URBANA 

Q.630.7IL6B  C001 

BULLETIN.  URBANA 
166-181  1914-15 


30112019528436 


*' 


£*•«*,  lv 

_* 

kf1 


